The elucidation of cell signaling pathways and protein oligomerization mechanisms will lead to a better understanding of disease as well as cellular homeostasis. Since essentially all biochemical interactions involve protein ligand interactions, the development of efficient methods of detecting these interactions is critical. The novel phage display system proposed here will enable the detection of protein-protein interactions in solution in a single reaction. This will be an improvement over the current technology that often requires five to six rounds of enrichment and can be plagued by isolation of non-specific phage clones. The high efficiency that is predicted in this system will come about by interaction-dependent selective infection of bacteria by phage encoding the interactor. In this feasibility study, we will construct the reagents required to show that an infective phage can rescue the infectivity of a non-infective phage by means of a protein-protein interaction. This system will consist of a bait phage and prey phage. Upon a successful interaction, the prey phage will be able to infect F' E. coli. These two phage populations will be encoded by plasmids with separate antibiotic resistance markers. To retrieve positive binders, the infected bacteria will be selected on the antibiotic marker encoded by the prey phage. PROPOSED COMMERCIAL APPLICATIONS: Commercialization of the components of the system described here could lead to more efficient phage display systems for library screening. Conventional, single phage systems could be improved by utilizing the data presented as preliminary support of this concept. Full development of this system could lead to a new generation of more efficient phage display systems that would allow easier high throughput screening of libraries for protein- protein interactions.